1. Field of the Invention
This invention relates to a method for cooling an aluminum strip heated for annealing.
2. Description of the Prior Art
In prior arts, in the case where an aluminum strip (The aluminum strip herein termed is a thin and lengthy bandlike aluminum plate continuously rolled by a rolling mill. The thickness of the aluminum plate is normally less than 3 mm, and the plate has various widths.) is subject to heat treatment for the annealing, the aluminum strip in the form of a coil is introduced into a batch type furnace such as a bell type furnace and annealed in a well-known method. In accordance with this method, since the strip is wound into a coil-like form, there is a one portion, i.e., the surface which tends to be affected by heat, and the other portion, i.e., the central portion which is hard to be affected by heat so that the quality therebetween is uneven.
A method has been proposed in order to overcome such a drawback noted above, which method comprises paying off successively an aluminum strip in the form of a coil from one end thereof, passing the paid-off strip in its floating condition through a heating zone to heat the strip to a temperature as indicated at 51 in FIG. 9, and passing it through a cooling zone to cool the strip to a temperature as indicated at 52 in FIG. 9. However, if the aluminum strip used is thin, it has a low elastic limit. Therefore, when such a thin strip is heated and cooled by the method as described above, thermal stress as shown in FIG. 10 occurs in the strip and the thermal stress exceeds the elastic limit, as a consequence of which strain, namely, wrinkles in parallel with the moving direction of the strip, in other words, the longitudinal wrinkles 53 as shown in FIG. 11 appear, thus giving rise to difficulties in that the products are diminished in value.